It has long been the practice in motor vehicles, such as automobiles and trucks, to suspend engines, and other heavy components that generate vibrations when operating, on resilient mounts that isolate and damp the vibration from reaching the passenger compartment of the vehicle. It is desirable in such circumstances to provide a mount that is relatively soft for low amplitude higher frequency vibrations, such as those produced while an engine is operating at idle speed or at a constant speed while the vehicle is cruising along on a smooth road. Making the mount too soft, however, results in a structure that may not be capable of damping the motion of a heavy mass, such as the engine, when the vehicle is traveling over a bumpy road.
The competing requirements for a mount that is soft enough to isolate low amplitude vibrations generated by an engine at idle, and yet is robust enough to damp and limit the movement of an engine relative to the vehicle chassis when the vehicle is encountering a bumpy road surface, have caused the designers of resilient mounts to employ hydraulic fluid flowing between multiple chambers within the mount, together with judiciously sized orifice tracks and fluid valve arrangements providing fluid communication between the chambers, to provide mounts that exhibit different damping performance dependent upon the magnitude and frequency of the vibratory input to the mount, without any active external control of fluid flow between the various chambers. Such mounts are known as passive hydraulic mounts. However, in trying to achieve a balance between controlling high frequency vibrations and low frequency vibrations, the range of damping possible with passive hydraulic mounts is reduced.
One method of broadening the range of frequencies a mount is effective over is by employing an active control mount. Active control mounts include an electrically activated control to dynamically change the damping ability of a mount. Often, though, these mounts are costly and complex, leading to significant restrictions in the number of applications within which the mount can be employed.
What is desired, therefore, is an improved bi-state hydraulic mount that overcomes these and other disadvantages.